1. Field of the Invention
Generally, the present invention relates to heat transfers in semiconductor processing systems. More specifically, the present invention relates to the application of thermoelectric devices for heating and cooling various components, structures or surfaces in a semiconductor processing system.
2. Background of the Related Art
A processing system generally comprises a plurality of process chambers having differing requirements for heating and/or cooling certain components or structures because individual components or structures within or attached to a process chamber reach an undesirable temperature under a variety of conditions, causing improper processing on substrates. Generally, because the temperature of the substrate affects the processing results on the substrate, it is important to maintain the temperature of the substrate within a desirable range for proper processing. Particularly, in an etch chamber where a process gas, such as argon, bombards the substrate and generates heat on the substrate, the temperature increase of the substrate must be controlled because the substrate has a thermal budget that must not be exceeded. When the thermal budget of the substrate has been exceeded, such as by heating the substrate above a particular temperature, improper processing results on the substrate, and device failure occurs.
An example of a component of a process chamber having both a cooling and a heating requirement is an electrostatic chuck (E-chuck) for holding a substrate in place during processing. Usually, the E-chuck physically contacts the substrate and the temperature of the substrate is affected by the temperature of the E-chuck. Thus, it is important to control the temperature of the E-chuck because the temperature of the substrate usually affects the processing results. Likewise, the temperatures of other components and structures of the processing chamber, such as valves, also need to be controlled because some processes exhibit optimum performance only at specific and/or narrow temperature ranges.
Another problem associated with temperature control is that temperature changes of the process chamber and/or its components may cause some deposited particles to be released back into the process chamber or some material on or in the substrate to flow or migrate, resulting in a defective circuit or other structures formed on the substrate. Thus, there is a need to remove these particles from the process chamber to prevent contamination on the substrates. Additionally, a lack of temperature control may cause a degradation of the process chamber walls or components.
In an attempt to control the temperature of the E-chuck, a fluid is flowed through a small chamber or channel in or under the E-chuck. The fluid is heated or cooled in a remote heat exchanger unit disposed externally and remotely from the process chamber. The same fluid may heat or cool the E-chuck depending on the temperature of the fluid released by the heat exchanger unit. However, this temperature management technique responds slowly to temperature changes at the E-chuck because the temperature of the fluid is measured at the heat exchanger and the corrective actions take place at the heat exchanger, remotely from the E-chuck.
Other attempts to control the temperatures of the components of a processing system use remote thermal electric heat exchangers. A thermoelectric (TE) device transfers heat according to the Peltier effect. When a current is passed through a junction of two dissimilar conductors, the Peltier effect causes a temperature change that is proportional to the current through the junction. One end of the conductor becomes cold while the other end of the conductor becomes hot. This well-known principle can produce temperature differentials of up to 100.degree. F. and can cool the cold end of the conductor even below the freezing point of water. One example of a TE device is the DuraTEC available from Marlow Industries, Inc., Dallas, Tex. A TE device may be used with a fluid to flow heat to or from a remote object, so the TE device can heat or cool the object remotely, as in a heat exchanger. Examples of such uses are described in the following United States Patents.
U.S. Pat. No. 5,613,364 describes a temperature control module for heating or cooling part or all of the interior of a process module. The temperature control module is mounted on the exterior of the process module and has a thermoelectric heat exchanger assembly, remote from the internal space of the process module, using a dielectric liquid that flows in and out of the process module to cool or heat the inside of the process module. The temperature control module also has a temperature sensor for sensing the temperature of the dielectric liquid as the liquid flows into the temperature control module, thereby indicating the temperature in the process module.
U.S. Pat. No. 5,154,661 describes a thermal electric cooling system for cooling a wafer chuck or a developer cooling tank. The thermal electric cooling system is located remotely from the wafer chuck or the developer cooling tank. The thermal electric cooling system includes a cooling reservoir for cooling a coolant fluid that circulates to the wafer chuck or developer cooling tank. A temperature sensor is located in the cooling reservoir for providing feedback regarding the temperature of the coolant fluid, so that a controller can adjust an array of thermal electric cooler cells to maintain the coolant fluid at a particular temperature.
U.S. Pat. No. 5,029,445 describes a thermal electric cooling system for maintaining a predetermined liquid temperature in a liquid bath in a wet process station for processing semiconductor wafers. The thermal electric cooling system is located remotely from the liquid bath and the wet process station. The thermal electric cooling system has an inlet and an outlet for circulating cooled liquid to the wet process station. The thermal electric cooling system also has a heater for heating the liquid after it has been cooled by the thermal electric cooler to raise the liquid temperature to a desired level. The temperature of the heater is sensed by a thermistor to provide temperature feedback to a controller.
U.S. Pat. No. 5,450,726 describes a thermal electric air cooling apparatus for use with climate or environmental control systems in the semi-conductor and other industries. As in the previously described cooling systems, the thermal electric air cooling apparatus is located remotely from the structure or space which it cools. An inlet and an outlet permit the air to circulate to and from the thermal electric air cooling apparatus. A heater may heat the air, so that the combined performance of the heater and the cooling apparatus can maintain the temperature of the air at a desired temperature. A thermocouple detects the temperature of the air at the outlet from the thermal electric air cooling apparatus to provide temperature feedback to a controller.
However, the applications for TE devices described above are inefficient for heating or cooling structures within a semiconductor processing system because they are located remotely from the part being heated and/or cooled. Considerable heat loss or gain may occur between the heat exchanger and the structure, resulting in a less than optimum usage of the TE device's heat transfer capability. Additionally, since the TE device is disposed remotely from the structure, there is a built-in delay in the response time of the TE device to the changes in temperature at the component of the processing system. Furthermore, a coolant fluid flowing from a remote heat exchanger into the processing system and around or near the structure to exchange heat with the structure exhibits a temperature variation or gradient along its flow path, so the structure is not cooled or heated uniformly.
Therefore, a need exists for a processing system that provides a more exacting control and a faster response to temperature variations in particular components of the processing system. It would be desirable if the processing system has a better heat transfer capacity at the heated component to allow immediate correction to temperature variations. There is also a need for a system that removes contaminant particles from the process chamber to prevent contamination on the substrates.